1. Field of the Invention
The present invention relates to a technology for controlling a distance and a directivity of a radio communication.
2. Description of the Related Art
A radio frequency identification (RFID) tag is currently commercialized and increasingly in use in a field of physical distribution. For example, a system for managing goods or products stored in a warehouse or the like by using the RFID tag is disclosed in Japanese Patent Application Laid-Open No. 2000-113077.
The RFID tag is also called an integrated circuit (IC) tag, which stores therein various data and performs a radio communication with a reader/writer that performs a data read/write with respect to the RFID tag.
A communication range between the RFID tag and the reader/writer and a directivity of a communication radiowave vary depending on a variation in conditions, such as output level of the radiowave of the REID tag, antenna size, antenna wiring, and antenna type.
In other words, if it is required to perform a communication with a reader/writer located in a remote place, or to adjust the directivity of the communication radiowave, the RFID tag needs to be replaced with other type of RFID tag suitable for each condition to achieve a desired result.
However, with a conventional technology described above, when it is required to control the distance or the directivity of the radio communication in a place where the RFID tag is installed, it is difficult to respond to such requests in an expedited manner.
Specifically, because substances such as metal and moisture existing in the place where the RFID tag is installed cause a disturbance of the radio communication, it is necessary to adjust the distance and the directivity of the radio communication depending on an environment of the place for realizing a stable radio communication.
In this case, for adjusting the distance and the directivity of the radio communication, it is necessary to replace the RFID tag with other type of RFID tag suitable for a desired condition, which necessitates preparation of various types of RFID tags in advance.
Thus, there is a demand to easily and effectively control the distance and the directivity of the radio communication without performing cumbersome operations, such as an operation of replacing the RFID tag.